ceph: fix snap rebuild condition

We were rebuilding the snap context when it was not necessary
(i.e. when the realm seq hadn't changed _and_ the parent seq
was still older), which caused page snapc pointers to not match
the realm's snapc pointer (even though the snap context itself
was identical).  This confused begin_write and put it into an
endless loop.

The correct logic is: rebuild snapc if _my_ realm seq changed, or
if my parent realm's seq is newer than mine (and thus mine needs
to be rebuilt too).

Signed-off-by: Sage Weil <sage@newdream.net>

diff --git a/fs/ceph/snap.c b/fs/ceph/snap.c
index 8a43bc8..df04e21 100644 (file)
--- a/fs/ceph/snap.c
+++ b/fs/ceph/snap.c
@@ -314,9 +314,9 @@ static int build_snap_context(struct ceph_snap_realm *realm)
           because we rebuild_snap_realms() works _downward_ in
           hierarchy after each update.) */
        if (realm->cached_context &&
-           realm->cached_context->seq <= realm->seq &&
+           realm->cached_context->seq == realm->seq &&
            (!parent ||
-            realm->cached_context->seq <= parent->cached_context->seq)) {
+            realm->cached_context->seq >= parent->cached_context->seq)) {
                dout("build_snap_context %llx %p: %p seq %lld (%d snaps)"
                     " (unchanged)\n",
                     realm->ino, realm, realm->cached_context,